OPT 2500 Contact Lens Theory UNIT 1 Notes Flashcards
That does CPC Mean ?
Central Posterior Curve:
CPC and Base Curve Can Be Expressed in 2 ways, what are they?
Radius of Curvature and Diopters
What is the optical Zone of a contact Lens ?
The surface area of the contact lens Rx
The Shorter the Radius of Curvature…..
The Steeper the Base Curve and the higher the Diopteric Power.
What is the Formula for the conversion of Radius of Curvature to Diopters
D= N2-N1/R
What two things influence Vault ?
- Radius of curvature: The smaller the raduis the lager the vault
- Lens Diameter: The Larger the diameter the larger the vault
What are the surface power of a lens made of material with a refractive index 1.3375 and if the radius of curvature is 7.67mm ?
Index of Refraction of Material: 1.3375
Radius of Curvature: 7.67mm
Diopteric power: ?????
- So when you have a material (N2= 1.33375) being seen through Air (N1= 1) with a radius of curvature of (R= 7.67mm) you have a base curve that is 44.00 Diopters strong.
What Radius of curvature has a higher dioptric power 7.76mm or 7.34mm with the refractive index of a material = 1.33375
When compared to each other the one with a smaller radius of curvature had a higher dioptric power
7.76mm = 44.00D and 7.34mm = 46.00
What is Sagittal Depth or Height / Vault ?
sagittal depth or height of a lens is the distance between a flat surface and the back surface of the central portion of the lens.
Anything that increases theVault/Saggital Depth or height
Makes the lens steeper (tighter on the cornea)
The smaller the base curve the ___________ the lens is
Steeper
How do you make a lens fit tighter?
- Smaller/Shorter/Decreased Raduis of curvature (Base Curve)
or
- Larger/longer Diameter
How do you make a lens fit looser ?
- Larger/Longer/Increase Raduis of curvature (Base Curve)
or
- Smaller/shorter Diameter
Anything that decreases the Vault/Saggital Depth or height
Makes the lens Flatter (looser on the cornea)
HOW DO YOU MAKE A LENS FLATTER/LOOSER LENS?
LARGER BASE CURVE / SMALLER DIAMETER
To Flatten a Lens
- Increase [longer] the base curve radius
i. e. 7.50 mm to 7.55 mm - Decrease the lens diameter
i. e. 8.8 mm to 8.6 mm
HOW DO YOU MAKE A LENS STEEPER/TIGHTER LENS ?
SMALLER BASE CURVE and
LARGER DIAMETER
To Steepen a Lens
- Decrease [shorter] the base curve radius
i. e. 7.50 mm to 7.45 mm - Increase the lens diameter
i. e. 8.8 mm to 9.0 mm
If the base curve of a contact lens was fitted as 7.70 mm then changed measuring 7.60 mm what is the change in dioptric power? USE THE RULE OF THUMB
Ex 2: If the base curve of a contact lens was fitted as 7.70 mm then changed measuring 7.60 mm what is the change in dioptric power? USE FORMULA
What its the IPC and what is it for ???
IPC: Intermediate Posterior Curve
- Is the curve between the Base and the Peripheral
Curve.
- The IPC allows the lens to move over the flatter
regions of the cornea with digging in.
- It also allows the tears to flow underneath the contact lens
- The Radius is approx 1mm (base curve of IPC) is
longer/larger then CPC (Central Posterior Curve).
This means that the IPC flatter then the CPC.
- Flushing out debris and bring fresh oxygen to the cornea
What 3 type of blends for curve junctions ?
- Heavy (can’t really see blend)
2. Medium (borders are semi-identifiable)
3. Light (borders are identifiable)
Why are blends used ?
- Smoothes Junctions between curves so there is no irritation due to the sharp junctions
- Helps reduce debris build up at the junctions
How much are soft contact lenses suppose to go beyond the cornea ?
1 mm beyond the cornea
